With High Density loads, velocity is less of a concern.. When you say "heavy shot" are you meaning the 3 inch 1 5/8 loading of Federal Heavyweight 5s? If you are, than you are shooting the fastest heavier than lead load available.. Hevi Shot debuted their Mag blend 5,6,7 shot but only stepped up the velocity to 1200..

If you are shooting the Fed Heavyweight in 5s, I would urge you to get away from the 5s and drop down to the 7s.. At the blistering 1300fps, the 7s will kill longer than you should be shooting and they should help to increase your pattern density due to more pellets.